The present invention relates to a pickup stylus body for capacitance disk records and a method for making such stylus bodies.
Pickup styluses for use with capacitance disk records comprises diamond body and an electrode attached thereto which senses the geometric surface variations of the record as capacitance variations. The electrode is conventionally formed by vacuum deposition, sputtering, or ion plating a conductive material such as hafnium or titanium. Since such conductive material is chemically different from the underlying material, the electrode is only physically attached to the underlying body, resulting in an electrode having a tendency to separating therefrom during use due to friction with the record surface.
Copending U.S. patent application No. 268,888 filed June 1, 1981 (now U.S. Pat. No. 4,409,712) assigned to the same assignee as the present invention discloses a method for making a stylus for capacitance disk records. The disclosed method involves placing a diamond body in a virtually vacuum or inert gas containing a small amount of oxygen and heating the diamond at an elevated temperature so that the carbon atoms of the surface area are converted to a layer of conductive carbon. The conductive layer is subsequently lapped into an elongate form so that it extends to the stylus's contact face to serve as a pickup electrode. Since the conductive carbon layer is integral with the diamond body, the electrode is not separable therefrom and resistant to wear.
Conventionally, the diamond body is placed on an end of a titanium body with a silver paste deposited therebetween and heated in a vacuum at an elevated temperature to fuse the silver paste for soldering the diamond and titanium bodies. However, the application of heat in the presence of small amount of oxygen during the subsequent diamond's surface conversion causes the titanium body to oxidize and causes the silver paste to melt, resulting in styluses unsuitable for satisfactory operation. Alternatively, use of a single body of diamond as large as 1 mm in length could eliminate this problem. However, the diamond of this size is only available naturally at a prohibitively high cost.